Sciatica | Causes and Risks

Sciatica refers to inflammation, compression or irritation of the large sciatic nerve running from the low back down the legs. But what triggers this nerve pain in the first place? Lets discuss the various spinal problems that can affect this important nerve.

Sciatic Nerve Review

The sciatic nerve originates from the lower lumbar spinal cord, specially nerve roots L4 through S3. It travels through the pelvis, exits via the sciatic foramen, passes under the piriformis muscle and runs down the back of each thigh, providing nerve supply to the posterior legs.

Anything causing inflammation or compression of this long nerve pathway can result in sciatica.

Herniated Discs – A Common Culprit

One of the most frequent triggers of sciatic pain is a herniated disc (also called ruptured or slipped disc) in the lumbar spine. This happens when the jelly-like disc nucleus pulposus leaks out and irritates nearby nerve tissues. Patients often recall a popping sensation at the onset of symptoms.

During such disc ruptures, bits of nucleus material can physically touch nerve roots exiting the spine, resulting in inflammation and sciatic nerve irritation. The body also responds by releasing inflammatory chemicals around affected nerves, worsening their irritation.

Since the L4-L5 and L5-S1 spinal levels interface with nerve roots converging to form the sciatic nerve, their discs are most often involved.

Bulging discs can have a similar effect by compressing nerves in the spinal canal, especially when inflamed.

Degenerative Disc Issues

Degenerative disc disease is part of the normal aging process, causing discs to gradually lose hydration and elasticity over decades of wear-and-tear.

As discs degenerate, shrink and grow stiffer, they lose their ability to act as shock absorbers between vertebrae. This can stress nearby joints, ligaments and nerves. Inflammation ensues, then sciatic pain flares up. Degenerative changes also encourage disc bulging and herniation.

Middle-aged and elderly patients often develop sciatica as discs naturally thin over time, even without a single traumatic event.

Spinal Stenosis

Spinal stenosis refers to abnormal narrowing of the bony spinal canal due to arthritis, disc bulging, enlarged facet joints or ligamentum flavum thickening. This reduces space available for the spinal cord and traveling nerve roots.

When severe stenosis compresses lumbar nerve roots, patients feel classic sciatica symptoms from L4, L5 or S1 nerve inflammation down the legs. Nerve fibers get directly squeezed and also choked of oxygen supply.

Stenosis-related sciatica tends to come on gradually as arthritis slowly worsens over years. Symptoms get provoked by walking longer distances as nerves get repeatedly pinched with activity then inflammation flares.

Spondylolisthesis

Spondylolisthesis means one vertebra slipping forward abnormally in relation to another, frequently at the L5-S1 junction. This creates a shearing effect on nearby nerve roots. Foraminal stenosis also develops, compressing nerves as they exit the spinal canal.

The slipping vertebral segment may even fracture a bit, releasing inflammatory particles that directly irritate adjoining nerves. Muscle spasms often accompany the injury too, worsening nerve compression.

Degenerative spondylolisthesis develops slowly with age-related wear on spinal joints. Traumatic types happen suddenly after accidents. Both inflame nerve roots including those forming the sciatic nerve.

How Injuries, Muscles, and Masses Can Cause Sciatica

In some cases, sciatica is triggered not by spinal arthritis or disc disease, but by extrinsic factors irritating nerves. These include:

Traumatic Injuries

Falls, accidents, sports collisions, or blows to the spine can abnormally stretch or compress lumbar nerve roots, inciting inflammation. Discs may rupture after trauma as well. Fractures fragmenting near nerve tissues further enflame them.

Lifting with improper body mechanics similarly strains soft tissues surrounding nerves. Twisting awkwardly while bearing weight, or lifting heavy objects above waist height risks disc protrusions and small tears in ligaments allowing inflammatory substances to contact nerves. Skilled manual professions and athletic endeavors prone to injury demonstrate higher rates of sciatica.

Muscle Tension

Muscles, like the piriformis and hamstrings, run adjacent to sciatic nerve branches descending the rear hip and thigh. Their anatomical proximity allows taut muscles to physically squeeze and trap nerve components after overuse strain.

Piriformis syndrome is a common culprit, especially among runners and cyclists who overwork hip external rotators. The inflamed, spastic piriformis clenches onto the sciatic nerve eliciting similar symptoms but different anatomical origin than disc-related sciatica. Trigger points in the hamstring muscles can also contribute to nerve compression.

Mass Lesions

Rarely, abnormal tissue growths or collections in the spinal canal externally compress nerves at the lumbar levels. These include:

• Epidural abscesses: infections near the spinal nerves
• Hematomas: blood clots from bleeding disorders, anticoagulant use, or trauma
• Tumors: malignant metastases or benign masses like osteochondromas

By applying pressure against nerve structures, these space-occupying lesions physically pinch nerves. They also leak inflammatory substances onto nerve roots or within the cerebrospinal fluid, inciting swelling and pain.

Further irritation of nerve roots going on to coalesce as the sciatic nerve provokes corresponding symptoms down the legs. Careful assessment of risk factors and advanced imaging can distinguish these unusual causes from typical mechanical spinal issues behind most sciatica cases.

Conclusion

In essence, traumatic insults, muscles seizing sciatic nerve branches, and extraneous masses impacting lumbar nerve roots all elicit inflammation contributing to sciatic symptoms much like degenerative spinal causes.

Hopefully this gives some insight into what causes sciatica – a range of lumbar spine problems affecting this important nerve structure. While symptoms are uncomfortable, the outlook for resolution is often good with appropriate management.